As is well known, heavy duty road vehicles, such as trailer tractors, employ compressed air brake systems. Such pneumatic or air braking systems generally involve an air compressor operable in normal or unloading modes, a governor for controlling the operating cycle of the air compressor, an air dryer and a reservoir for holding pressurized air for delivery to the vehicle brakes. Air for the pneumatic brake system is supplied from the air intake manifold of the vehicle engine. The vehicle may or may not be equipped with a turbocharged or supercharged internal combustion engine from which engine exhaust gases at high temperatures are discharged through an exhaust stack.
When the pressure in the air reservoir falls below a predetermined minimum pressure, say about 100 psig, the compressor governor then causes the air compressor to operate in a normal or loading mode to compress air. The compressed air from the air compressor during its normal or compressing cycle is passed through an air dryer to remove moisture and contaminants and then into the air brake reservoir or reservoirs. The air dryer contains a filter/desiccant for removing contaminants and moisture from the air introduced therein. When the desired pressure, say about 120 psig, is attained in the pressurized air reservoir, the compressor governor functions to cause the air compressor to unload (unloading mode). When the compressor operates in the unloading mode the intake air from the vehicle engine manifold passes through the compressor, but is not compressed therein.
During the unloading stage of the compressor air flows reversely through the dryer for purging the filter/desiccant in the dryer of contaminants and moisture accumulated therein. Such reverse flow and purging may continue until the governor device restores the compressor to its cut-in or compressing mode. The purge air discharges from the dryer to the atmosphere periodically with force carrying with it the contaminants and moisture which have accumulated in the dryer. While discharge of moisture to the atmosphere is not particularly harmful, discharge of other contaminants such as oil droplets and oil-coke particles creates environmental pollution problems by being deposited on the ground or on roads. These contaminants being toxic and flowable in nature present safety hazards also. Because of the high lubrication requirements in air compressors, contamination of the compressed air with lubricating oil and oil-coke contaminants is significant.